1. Field of the Invention
The present invention generally relates to a gas lift plunger assembly for use in a gas-producing well and, more particularly, is concerned with pad plunger assembly with interfitting keys and key ways on a mandrel and pads of the plunger assembly.
2. Description of the Prior Art
Gas-producing wells typically employ a plunger disposed within tubing of the well and capable of traveling vertically in the tubing as the well is cycled between shut-in and opened conditions in a manner well-known to one of ordinary skill in the art. The plunger is freely movable vertically in the well tubing and is adapted to rise vertically under the force of sufficient gas pressure to drive or lift the plunger and a slug of liquid, such as oil, above it to the surface while isolating the base of the liquid slug from the gas which lifts the plunger. The plunger falls by gravity back down the tubing of the well after the slug of liquid has been delivered to the surface and the gas pressure in the well tubing has decreased due to the transmission of gas from the well tubing to a suitable storage location.
One prior art plunger assembly, called a pad plunger assembly, has an elongated rigid non-flexible central rod or mandrel and a pair of end members attached to the opposite ends of the mandrel. Between the opposite ends of the mandrel, the plunger typically has one or more subassemblies of three spring-loaded interlocking pad sections thereon. The spring-loaded pad sections can expand outwardly from and contract inwardly toward the mandrel to compensate for any irregularities in the tubing thus creating a moving frictional seal with the well tubing.
A problem exists, however, with the above-described prior art plunger assembly. There is a tendency for oil and gas to flow beneath the pad sections along the mandrel such that the plunger assembly loses its sealing efficiency. Consequently, a need exists for an innovation in the construction of the pad plunger assembly which will provide a solution to the aforementioned problem without introducing any new problems in place thereof.
The present invention provides a pad plunger assembly designed to satisfy the aforementioned need. The plunger assembly of the present invention provides interfitting elements on the pad sections and mandrel of the assembly which impede the ability of oil and gas to flow along the mandrel beneath the pads from one end to the other end thereof. Such elements solve the aforementioned problem with the prior art plunger assembly design.
Accordingly, the present invention is directed to a pad plunger assembly which comprises: (a) an elongated mandrel having a pair of opposite ends; (b) at least one pad subassembly disposed about the mandrel between the opposite ends thereof; (c) a plurality of annular key ways and annular keys respectively defined on the mandrel and pad subassembly, the key ways and keys interfitting with one another so as to impede the ability of a fluid to flow along the mandrel and beneath the pad subassembly adjacent to the mandrel and from one to the other of the opposite ends of the mandrel; and (d) means for securing the pad subassembly on and around the mandrel.
More particularly, the annular key ways are annular grooves defined about and extending into an exterior surface of the mandrel. The annular keys are annular ridges defined on and protruding outwardly from pad sections of the pad subassembly.
These and other features and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described an illustrative embodiment of the invention.